Slab transfer apparatus

ABSTRACT

There is disclosed herein a plurality of aligned induction heaters which are open at both the top and bottom, lift means for partially ejecting a heated slab from each heater and receiving a cold slab, crane and hoist means for picking up a slab at any heater and transferring it to an outgoing conveyor, and crane and hoist means for picking up a cold slab from an incoming conveyor and delivering the same to a heater.

United States Patent R NN C 00 l 4 2 M m m w "n "w imn k m u n06 B a h Tn FAS L 66 666 999 H8 111 n ///.H 452 mm mm 754 395 t WM 831 at 759 mBnU 233 PA 6 0 4 4 4 0 .l h 0 y M e r r um mC r 9 L 7 w kfl i m AJ 20 28%B27 h T d m N. 6 NMR m fla I AFP l. ltll. 2 25 7 HUM.

Attorney-J. H. Slough [54] SLAB TRANSFER APPARATUS 11 Claims, 6 DrawingFigs.

ABSTRACT: There is disclosed herein a plurality of aligned inductionheaters which are open at both the top and bottom, lift means forpartially ejecting a heated slab from each heater and receiving a coldslab, crane and hoist means for picking up a slab at any heater andtransferring it to an outgoing conveyor, and crane and hoist means forpicking up a cold slab from an incoming conveyor and delivering the sameto a heater.

[56] References Cited UNITED STATES PATENTS 1/1929Kehren.........................

illutallllllli PATENTEU JAN 5 1971 SHEET 1 UF 5 INVENTOR. Bruce 5McAr-zhur 1/- @LOUGH A TTORNE y PATENTEU JAN 5 l97| M/L 4 DEM/4 M0INVENTOR. Bruce E JH. nous/1 PATENTEDJAN 51971 3553414 SHEET 3 8F 5 I kgINVENTOR. 5mm 6 E fifc/irf/iur J H. SLOUGH A TT'OR/VEY PATENTEDJAN 5:9713,553Q4ld I saw u UF 5 INVENTOR. Bruce E Mc/lr Zhur BY )1. SAOUGHATTORNEY PATENTEU JAN SIS?! 3.553414 SHEET 5 m: S

INVENTOR Bruce E McArf l/GH ATTORNEY SLAB TRANSFER APPARATUS Thisinvention relates to the induction heating of metal and particularly toapparatus for loading and unloading a plurality going conveyor at theother end of the line. The heaters are disposed over open pits orrecesses containing lift means for raising a workpiece at leastpartially above the upper end of the heater whereby it can be engaged byhoist means. Cold slabs are brought into the system by the incomingconveyor and are transferred to the individual heaters by a loadingcrane and hoist or fork means whereby the workpieces are heated to thedesired temperature. An unloading crane and hoist or the above-mentionedfork means pick up the heated workpieces and transfer them to theoutgoing conveyor to be delivered to a mill.

The present invention is particularly directed to and adapted'for thehandling of workpieces in the form of elongated slabs of metal having agreater length than width and a greater width than thickness, said slabsbeing disposed on one side edge during heating and transfer to and fromthe conveyor.

An important object of the invention is to provide means for heating anelongated slab of metal positioned on one side edge by introducing theslab into the top of an induction heater disposed on a vertical axis andremoving the slab from the top of the heater.

Another object of the present invention is to provide apparatus forsystematically heating workpieces in a plurality of induction heaterswhereby a fully heated slab is always available upon mill demand andeach heater is promptly reloaded upon removal of the heated workpiece.

Another object of the invention is to provide improved means forefficiently loading and unloading elongated slabs of metal in aplurality of induction heaters.

Still another object of the invention is to provide apparatus as setforth above including control means for maintaining a continual movementof the slabs into and out of the system.

Other objects of the invention and the invention itself will be readilyunderstood from the following description thereof and the accompanyingdrawings, in which said drawings:

FIG. I is a semischematic elevation of the heaters, conveyors and craneand hoist means of a first form of the invention, the heaters beingshown in cross section for purposes of clarity;

FIG. 2 is a transverse section takenalong the line 2-2 of FIG. 1;

FIG. 3 is a simplified diagram of control means for the slab transferapparatus;

FIG. 4 is a semischematic elevation of a second form of the invention;

FIG. 5 is a view similar to FIG. 4 showing the parts thereof indifferent operative positions; and

FIG. 6 is a vertical section taken along the line 6-6 of FIG. 5.

Referring now tothe drawings in all of which like parts are designatedby like reference numerals, FIG. 1 shows a plurality of like inductionheaters 10a, 10b, 10c, and 10d. Each heater is provided with aninduction coil 11 defining an opening adapted to receive an elongatedslab 12 which has a greater length than width and a greater width thanthickness and which said slab is disposed on one side edge whereby thewidth thereof becomes its vertical dimension. The heaters are open atboth the top and bottom and are disposed above an open pit or recess I3wherein there are mounted a plurality of hydraulic lifts 14 havingupwardly projecting piston rods 15. As shown in FIG. 2, two lifts 14 areprovided beneath each of the heaters, the upper ends of the piston rods15 thereof carrying an elongated slab support 16 adapted to receive oneof the slabs I2 disposed edgewise thereon. FIG. 2 shows the nonnalheating position of the lifts 14 wherein the slab 12 is substantiallyaxially centered with respect to the induction coil II where it remainsstatic during heating.

Adjacent to the first heater there is provided an incoming conveyor 20by means of which cold slabs 12 are initially introduced into thesystem. Adjacent to the heater 10d, there is provided an outgoingconveyor 21 by means of which a heated slab 12, as shown in broken linesin FIG. 1, is conveyed to the mill upon demand.

The means for loading and unloading the heaters l0a-I0d also include apair of laterally space I-beams 25 and 26 across which overhead cranes27 and 28 are mounted. The cranes 27 and 28 are identical inconstruction although different in function, the crane 27 serving as aheater loading crane and the crane 28 serving as a heater unloadingcrane. These cranes may be of any conventional form and as hereindisclosed comprise end housings 29 adapted for rolling engagement withthe lower flanges of the I-beams 25 and 26 by means of beveled wheels30. Each housing 29 also carries pulley means 31 supporting downwardlydirected cables 32 having conventional lifting grabs 33 at their lowerends. The pulley means 3I may be synchronously driven by a reversiblehoist motor 34 whereby the grabs 33 can be raised and lowered in aconventional manner, and the cranes are driven along the I-beams bysuitable motors 34a.

The grabs 33 are of a known type having parallel gripping jaws 35connected by parallel acting linkage 36 the upper ends of which arepivotally carried by U-shaped cable retainers 37. As shown in FIG. 2,the retainers 37 are preferably connected by a stabilizing means 38 toprevent the grabs from twisting relative to each other.

As illustrated in FIG. I, the grabs 33 are of the type which openautomatically when the weight of the jaws 35 is taken off of the linkage36 and which, conversely, tighten or move inwardly with a forceproportional to the load disposed between said jaws. The weight of theslab 12 carried by the grabs 33 of the loading crane 27 in FIG. 1 causesthe jaws 35 thereof to grip the said slab sufficiently so that the samemay be lifted by operation of the hoist means. On the other hand, thegrabs 33 of the unloading crane 28 have the jaws 35 thereof in the openposition while resting on top of the heater 10b, the angle of thelinkage 36 flattening in a horizontal plane to allow this openingmovement. It will be noted that the upper ends of the heaters l0al0d areprovided with protective guide stops 39 extending slightly inwardly oftheheater opening. The inner ends of said guide stops are provided withdownwardly and inwardly angled, sloping guide surfaces 390 for directingthe lowering slab toward the center of the heater. By providing areduced opening at the top of each heater, the guide stops 39 ensurethat a slab inserted into the heater will not tough or damage the innerwalls of the heater. Said guide stops also provide striking or abutmentmeans for receiving the lower ends of the jaws 35 to cause them to open.It will be further noted that similar guide stops 40 and 41 havingsloping guide surfaces 400 and 41a, respectively, are provided on eitherside of the conveyors 20 and 21, respectively, to cause opening of thegrabs 33 when they are lowered over said conveyors.

In operation, all of the heaters I0a-l0d are initially loaded by theloading crane 27. This is effected by lowering the grabs 33 thereofdownwardly onto the guide stops 40 whereby the jaws 35 open up. Theconveyor 20 can then convey a cold slab in between the jaws 35. When thegrabs 33 of said loading crane 27 are raised, the jaws 35 move inwardlyto pick up the slab whereby it can be conveyed to any one of theheaters. At any given heater, the lift 14 is actuated to move the pistonrods 15 and the slab support 16 upwardly to the position shown withrespect to heater 100 in FIG. 1. In this position, the cold slab can belowered onto the slab support 16, further lowering the hoist meanscausing the jaws 35 to open whereby the slab can be lowered to thenormal heating position of 10a, 10b, and and 10d.

When the slabs are heated and upon mill demand, the unloading crane 28picks up the heated slabs and transfers them to the outgoing conveyor21. To effect the unloading operation, the grabs 33 of the unloadingcrane 28 are lowered over the selected furnace to the positionillustrated in FIG. I wherein the jaws 35 open. The associated lifts 14then move the slab l2 upwardly to the position illustrated whereby thesame can be engaged by the grabs 33 for movement to the outgoingconveyor 21.

In the system and apparatus disclosed, it is desired that the heaters becontinuously loaded with cold slabs as the heated slabs are removed andtransferred to the mill. As shown in FIG. 3, a central or main control50 is adapted to receive control data or signals from the heaters al0dand from the mill indicating that a heated slab is to be transferred tothe outgoing conveyors 21. Broken lines 51 from the heaters indicate,for example, the transmission of temperature sensing information back tothe controls indicating which of the heaters contains a completelyheated slab. Broken line 52 indicates means for mill demand signals tobe transferred to the main control which will not effect delivery of aslab to the outgoing conveyor 21 unless such demand is made. The brokenline 53 indicates control signals which can be directed to the lifts 14to selectively actuate the same if a heated slab in a given heater is tobe raised to the position illustrated in FIG. 1 at heater 10c. Thebroken lines 54 and 55 represent control lines directed to the loadingcrane 27 and unloading crane 28, respectively, to actuate the same toremove a selected heated slab from a given heater and to load said givenheater with a cold slab.

The main or central control 50 may comprise computer storage and readout means for effecting a programed sequence of operations or maycomprise any other suitable, known control means. It will be readilyunderstood that the control 50 will actuate the unloading crane 28 onlywhen it is determined that there is a demand-from the mill and that oneof the slabs in one of the heaters has reached sufficient temperature tobe delivered to the mill. When the proper conditions are met, saidcontrol will actuate the unloading crane 28 to unload the heater andtransfer the slab to the outgoing conveyor 21. At the same time, theloading crane 27 will pick up a cold slab and move the same toward andinto the now empty heater.

The second embodiment of the invention as shown in FIGS. 46 alsocomprises a plurality of induction heaters arranged in a line between anincoming conveyor and an outgoing conveyor and includes a transfermechanism for synchronously picking up and depositing slabs at theheaters and conveyors The induction heaters are shown at 60a, 60b, 600,each heater comprising a frame 61, an induction coil 62, and arelatively thin inner refractory lining 63. Said heaters are bridgedacross a pit or recess 64 in which said recess are mounted a pluralityof hydraulic lifts 65 having upwardly acting piston rods 66 carryingslab supports 67 for raising and lowering slabs 12. As in the firstembodiment of the invention, the heaters 60a-60c are open at both thetop and bottom, and a lift 65 is provided beneath each heater fortransferring a slab between the full line, static heating position andthe broken line position shown in FIG. 4. The incoming conveyor isindicated at 68 and the outgoing conveyor is shown a at 69, and it willbe noted that both said conveyors are disposed at substantially the samelevel as the slab support when said slab supports are in their upper,broken line position.

The slabs 12 are transferred horizontally by means of an overheadtransfer mechanism 75 carried by a pair of laterally ,spaced, overheadI-beams 76 and 77. The mechanism 75 comprises pairs of horizontal sideframe members 78 and 79 transversely connected by cross beams 80 andadapted for rolling engagement with the lower flanges of said overheadI-beams by means of beveled wheels 81.

The framework comprising the side frame members and cross beams isprovided with four pairs of transversely aligned, downwardly projectingfork mounting members 83 and 84 adapted to guide vertically acting forks85. As best seen in FIG. 6, each pair of mounting members 83 and 84carries three forks 85, one fork being disposed midway between saidmounting members, and two endmost forks being slidably received in saidmounting members. Transverse braces 86 and 4 87 unitarily connect allthree forks for movement vertically as a unit. Means for the forks maycomprise any suitable' known mechanism, and as herein disclosed"includes a motor 7 I and gear transmission 88 mountedon'the-outer'sid'e'frame 1 member 79 and driving a shaft 89havingsprockets 90 and '91 carried thereby generally above the outermostforks 85. The lower ends of the fork mounting members 83 and 84 are'provided with sprockets 92 and 93 connected by chains 94'and95 to theupper sprockets 90 and 91'. It will be readily un' derstood, that thefork assembly is connected in anysuitable manner to the chains 94 and 95whereby rotation of the shaft 89 by the motor and gear transmissionmeans 88 causes the forks to move vertically. It will be further notedin FIG. 6 that the slab supports 67 are each provided with threerecesses or cutouts 95 extending transverse to the longitudinaldimension of the slab support adapted to receive horizontally projectingtines 96 of theforks 85.

Slab aligning hydraulic pushers 98 are mounted in opposed 100 are movedfrom their retracted position as shown in'FlG.

4 to the extended position shown in FIG. 5 whereby the enlarged endportions are brought against the sides of the slab 12. Thus any skewingof the slab is corrected before thesarne is lowered into the heaterthereby preventing'contact with and damage of the relatively thinrefractory liningl lt will be readily appreciated that in induction slabheaters, any space between the wall and the load is extremely costlyin'terms'of capacitors and efficiency. Therefore, only a minimum spacecan be provided in practice. .To keep this space at a minimum, therefractory lining mustalso be thin and cannot possibly stand beingscraped by a slab. Therefore, it is necessary to guide the slab in andout of the heater very precisely.

In operation, the overhead transfer mechanism 75 is mova v blehorizontally along the I-beams 76 and 77 between the full and dottedline positions of FIG. 5 by any suitable means such as a motor and geartransmission means 102 shown in FIG. 6.

The motor and gear transmission means 88 which drive the forks 85 aresynchronized to simultaneously movesaid forks between the dotted andfull line positions shown in FIGS. 4 and 5. The heaters 60a-60c areadapted to sequentially heat each slab 12 to successively highertemperatures whereby when the slab is finally removed from the heater60c and transferred to the outgoing conveyor 69, the same has reachedthe proper temperature to be received at the rolling mill. As

the slabs 12 of the heaters are indexed toward the right, a new slab istransferred from the incoming conveyor 68 to the number one heater 60a.7

Assuming an initial condition as shown in full line in FIG. 4wherein'each of the heaters contains a slab l2 and wherein the lifts 65are in the lowered position, upon demand from the mill, the forks 85 arelowered to the broken line position shown therein and the said lifts areactuated to raise the slabs to their uppermost position, also shown inbroken line. The motor and gear transmission means 102 is then actuatedto move the transfer mechanism to the right whereby the tines 96 movebeneath the slab 12 on the incoming conveyor 68'as well as the slabs ateach of the heaters. The tines of the forks disposed over the heaterscan, of course, enter the recesses or cutouts 95 in the slab support 67whereby they can pass under the slabs.

The slabs 12 are then lifted off of the slab support 67 to the elevated,broken line position of FIG. 5 whereby they can be indexed to the rightto place the new slab from the incoming conveyor over the first heater600, the slab from said first heater over the heater 60b,the slab fromthe heater 60b over the heater 60c, and the fully heated slab from thelast heater over the outgoing conveyor 69. The forks 85 are then loweredto deposit the slabs at the respective heaters and outgoing conveyor andat this time the pushers 98. are actuated to correct any skewing of theslabs disposed over the heaters. The transfer mechanism 75 is then movedrearwardly to clear the times from the slabs, and the pushers 98 areretracted whereby the lifts 65 can lower said slabs into the heater. Incontinuous operation, the forks 85 do not need to be returned to theneutral or raised position at the left of the heaters and conveyorsbetween transfers of the slabs since. adequate clearance is provided forthe forks to pass between the pushers 98 and similar clearance ispreferably provided at the conveyors by providing suitable breaks oropenings in said conveyors.

The present invention; that is, wherein an elongated load is positionedon one side edge and statically heated within an axially verticalheater, a lift mechanism is provided for at least partially projectingthe slab above the heater, and means are provided above the heater fortransferring the slab to an outgoing conveyor can readily be applied toa single heater if desired. However, the invention is particularly welladapted for use with multiple heaters used individually to completelyheat slabs, as shown in the first embodiment, or in a line of multipleheaters used for progressive or stage heating, as shown in the secondembodiment. It will also be understood that the transfer mechanisms asshown herein are disclosed only in their most simplified forms, theexact structural details thereofforming no part of the presentinvention.

It will be understood that many changes-in the details of the inventionas herein described and illustrated may be made without, however,departing from the spirit thereof or the scope of the appended claims.

Iclaim:

I. In a system for heating elongated metal slabsof greater length thanwidth and greater width than thickness disposed on one side edge, aplurality of induction heaters arranged in a line and disposed onvertical axes and open at the tops and bottoms thereof; lift meansprojecting upwardly through the bottom of each said heater forsupporting a slab in a first position within the heater for staticheating thereof; each said lift means being movable to a raised positionfor at least partially projecting a heated slab above the top of theheater and for receiving another slab; means for loading and unloadingthe slabs comprising overhead transfer means disposed for movement alongsaid line; an incoming conveyor at one end of said line for deliveringunheated slabs to a position to be picked up by said transfer means; anoutgoing conveyor at the opposite end of said line for receiving heatedslabs; control means for receiving a demand signal from a mill and fordetermining that at least one of the slabs in one of said heaters insaid line is completely heated; said control means including meansactuatingat least the lift means at said one heater to raise the heatedslab, and means actuating said transfer means to deliver the heatedslab'away from said line and onto said outgoing conveyor and to deliveran unheated slab from said incoming conveyor into said line.

2. In a system for heating elongated metal slabs of greater length thanwidth and greater width than thickness disposed on one side edge, aplurality of induction heaters arranged in a line; each heater disposedon vertical axes and open at the tops and bottoms thereof; lift meansprojecting upwardly through the bottom of each said heater forsupporting a slab in a first positionwithin the heater for staticheating thereof; each said lift means being movable to a raised positionfor at least partially projecting a heated slab above the top of saidheater and for receiving another slab; and means for loading andunloading the slabs from the top of each said heater comprising overheadtransfer means disposed for movement along saitl line; an incomingconveyor at one end of said line for delivering unheated slabs to aposition to'be picked up by said transfer means; and an outgoingconveyor at the opposite end of said line for receiving heated slabs,means for aligning each slab with each said heater when the slab isdeposited upon said lift means in raised position prior to each slabbeing lowered into each said heater.

3. In a system for heating elongated metal slabs of greater length thanwidth and greater width than thickness disposed on one side edge, aplurality of induction heaters arranged in a line; each heater disposedon vertical axes and open at the tops and bottoms thereof; lift meansprojecting upwardly through the bottom of each said heater forsupporting a slab in a firstposition within the heater for staticheating thereof; each said lift means being movable to a raised positionfor at least partially projecting a heated slab above the top of saidheater and for receiving another slab; and means for loading andunloading the slabs from the top of each said heater comprising overheadtransfer means disposed for movement along said line; an incomingconveyor at one end of said line for delivering unheated slabs to aposition to be picked up by said transfer means; and an outgoingconveyor at the opposite end of said line for receiving heated slabs;control means for receiving a demand signal from a mill and fordetermining the location of completely heated slabs in said heaters;said control means including means actuating a lift means at a selectedheater to raise a heated slab, means actuating said overhead transfermeans to deliver the heated slab of the selected heater to the outgoingconveyor and means actuating said overhead transfer means to pick up anunheated slab from the incoming conveyor and deposit said unheated slabin the empty heater.

4. In a system for heating elongated metal slabs of greater length thanwidth and greater width than thickness disposed on one side edge, aplurality of induction heaters arranged in a line; each heater disposedon vertical axes and open at the tops and bottoms thereof; lift meansprojecting upwardly through the bottom of each said heater forsupporting a slab in a first position within the heater for staticheating thereof; each said lift means being movable to a raised positionfor at least partially projecting a heated slab above the top of saidheater and for receiving another slab; and means for loading andunloading the slabs from the top of each said heater, said means forloading and unloading slabs comprising first hoist means fortransferring an unheated slab to an empty heater having the lift meansthereof in said raised position whereby said slab can be lowered to saidfirst position for heating; and second hoist means for engaging a heatedslab in raised positions and transferring said heated slab away fromsaid line.

5. In a system for heating elongated metal slabs of greater length thanwidth and greater width than thickness disposed on one side edge, aplurality of induction heaters arranged in a line having incoming and anoutgoing end; each heater disposed on vertical axes and open at the topsand bottoms thereof, lift means projecting upwardly through the bottomof each said heater for supporting a slab in a first position within theheater for a static heating thereof; each said lift means being movableto a raised position for at least partially projecting a heated slababove the top of said heater and for receiving another slab; and meansfor loading and unloading the slabs from the top of each said heatercomprising overhead transfer means disposed for movement along saidline; an incoming conveyor at one end of said line for deliveringunheated slabs to a position to be picked up by said transfer means; andan outgoing conveyor at the opposite end of said line for receivingheated slabs, said heaters adapted to successively heat slabs in saidheaters to progressively higher temperatures from the incoming to theoutgoing ends of said line; said lift means adapted to raise and lowersaid slabs simultaneously within said heaters; said means for loadingand unloading the slabs comprising overhead transfer means adapted tosimultaneously pick up all of the slabs in raised position, index eachslab to the heater of next higher temperature, move a new slab into theheater of lowest temperature, and move the slab from the heater ofhighest temperature away from said line.

6. In a system as set forth in claim 4: control means for receiving ademand signal from a mill and for determining the location of completelyheated slabs in said heaters; said control means including meansactuating a lift means at a selected heaterto' raise a heated slab,means actuating said second veyor at one end of said line for deliveringunheated slabs to a position to be picked up by said first hoist means;and an out going conveyor at the opposite end of said line for receivingheated slabs from said second hoist means.

8. In a system as set forth in claim 4: control means for receiving ademand signal from a mill and for determining the location of completelyheated slabs in said heaters; said control means including meansactuating a lift means at a selected heater to raise a heated slab,means actuating said second hoist means to deliver the heated slab ofthe selected heater to the outgoing conveyor, and means actuating saidfirst hoist means to pick up an unheated slab from the incoming conveyorand deposit said unheated slab in the empty heater.

9. In a system as set forth in claim 5: an incoming conveyor disposedadjacent to the incoming end of said line; an outgoing conveyor disposedadjacent tov the outgoing end of said line; said transfer means adaptedto pick up a slab at said in? coming conveyor and deposit a fully heatedslab at said outgo} ing conveyor with each indexing movement;

10. In a system as "set forth in claim 9; sa dp verhead transfer meanscomprising a plurality of yertically movable fork means connectedtogether in spaced i' valsequal to the spacing between said heaters andconveyors means for simultaneously lowering and raising said fork rne"fork means horizontally along line; said lift means adapted to projectsaid slabs above sa c l heaters whereby said fork means can be projectedundersla'bs at said incoming conveyor and said heaters, said slabs canberaised and moved to the next heater with one slab being moved away fromsaid line toward said outgoing conveyor and a 'new slab being introducedinto said line, said slabs can be lowered'to the lift means of the nextadjacent heater and said outgoing conveyor said lift means in raisedposition prior-to said slab being lowered into the heater.

s; means for moving said UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 3 553 414 l Dated January 5 1971 Bruce E. McArthurInventor(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet insert [73] assignee Ajax Magnethermic Corporation,Warren, Ohio, a corporation of Ohio Column 4, line 4 "Means for theforks" should read Means for propelling the forks 8S Signed and sealedthis 30th day of November 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer ActingCommissioner of Patent:

1. In a system for heating elongated metal slabs of greater length thanwidth and greater width than thickness disposed on one side edge, aplurality of induction heaters arranged in a line and disposed onvertical axes and open at the tops and bottoms thereof; lift meansprojecting upwardly through the bottom of each said heater forsupporting a slab in a first position within the heater for staticheating thereof; each said lift means being movable to a raised positionfor at least partially projecting a heated slab above the top of theheater and for receiving another slab; means for loading and unloadingthe slabs comprising overhead transfer means disposed for movement alongsaid line; an incoming conveyor at one end of said line for deliveringunheated slabs to a position to be picked up by said transfer means; anoutgoing conveyor at the opposite end of said line for receiving heatedslabs; control means for receiving a demand signal from a mill and fordetermining that at least one of the slabs in one of said heaters insaid line is completely heated; said control means including meansactuating at least the lift means at said one heater to raise the heatedslab, and means actuating said transfer means to deliver the heated slabaway from said line and onto said outgoing conveyor and to deliver anunheated slab from said incoming conveyor into said line.
 2. In a systemfor heating elongated metal slabs of greater length than width andgreater width than thickness disposed on one side edge, a plurality ofinduction heaters arranged in a line; each heater disposed on verticalaxes and open at the tops and bottoms thereof; lift means projectingupwardly through the bottom of each said heater for supporting a slab ina first position within the heater for static heating thereof; each saidlift means being movable to a raised position for at least partiallyprojecting a heated slab above the top of said heater and for receivinganother slab; and means for loading and unloading the slabs from the topof each said heater comprising overhead transfer means disposed formovement along said line; an incoming conveyor at one end of said linefor delivering unheated slabs to a position to be picked up by saidtransfer means; and an outgoing conveyor at the opposite end of saidline for receiving heated slabs, means for aligning each slab with eachsaid heater when the slab is deposited upon said lift means in raisedposition prior to each slab being lowered into each said heater.
 3. In asystem for heating elongated metal slabs of greater length than widthand greater width than thickness disposed on one side edge, a pluralityof induction heaters arranged in a line; each heater disposed onvertical axes and open at the tops and bottoms thereof; lift meansprojecting upwardly through the bottom of each said heater forsupporting a slab in a first position within the heater for staticheating thereof; each said lift means being movable to a raised positionfor at least partially projecting a heated slab above the top of saidheater and for receiving another slab; and means for loading andunloading the slabs from the top of each said heater comprising overheadtransfer means disposed for movement along said line; an incomingconveyor at one end of said line for delivering unheated slabs to aposition to be picked up by said transfer means; and an outgoingconveyor at the opposite end of said line for receiving heated slabs;control means for receiving a demand signal from a mill and fordetermining the location of completely heated slabs in said heaters;said control means including means actuating a lift means at a selectedheater to raise a heated slab, means actuating said overhead transfermeans to deliver the heated slab of the selected heater to the outgoingconveyor and means actuating said overhead transfer means to pick up anunheated slab from the incoming conveyor and deposit said unheated slabin the empty heater.
 4. In a system for hEating elongated metal slabs ofgreater length than width and greater width than thickness disposed onone side edge, a plurality of induction heaters arranged in a line; eachheater disposed on vertical axes and open at the tops and bottomsthereof; lift means projecting upwardly through the bottom of each saidheater for supporting a slab in a first position within the heater forstatic heating thereof; each said lift means being movable to a raisedposition for at least partially projecting a heated slab above the topof said heater and for receiving another slab; and means for loading andunloading the slabs from the top of each said heater, said means forloading and unloading slabs comprising first hoist means fortransferring an unheated slab to an empty heater having the lift meansthereof in said raised position whereby said slab can be lowered to saidfirst position for heating; and second hoist means for engaging a heatedslab in raised positions and transferring said heated slab away fromsaid line.
 5. In a system for heating elongated metal slabs of greaterlength than width and greater width than thickness disposed on one sideedge, a plurality of induction heaters arranged in a line havingincoming and an outgoing end; each heater disposed on vertical axes andopen at the tops and bottoms thereof, lift means projecting upwardlythrough the bottom of each said heater for supporting a slab in a firstposition within the heater for a static heating thereof; each said liftmeans being movable to a raised position for at least partiallyprojecting a heated slab above the top of said heater and for receivinganother slab; and means for loading and unloading the slabs from the topof each said heater comprising overhead transfer means disposed formovement along said line; an incoming conveyor at one end of said linefor delivering unheated slabs to a position to be picked up by saidtransfer means; and an outgoing conveyor at the opposite end of saidline for receiving heated slabs, said heaters adapted to successivelyheat slabs in said heaters to progressively higher temperatures from theincoming to the outgoing ends of said line; said lift means adapted toraise and lower said slabs simultaneously within said heaters; saidmeans for loading and unloading the slabs comprising overhead transfermeans adapted to simultaneously pick up all of the slabs in raisedposition, index each slab to the heater of next higher temperature, movea new slab into the heater of lowest temperature, and move the slab fromthe heater of highest temperature away from said line.
 6. In a system asset forth in claim 4: control means for receiving a demand signal from amill and for determining the location of completely heated slabs in saidheaters; said control means including means actuating a lift means at aselected heater to raise a heated slab, means actuating said secondhoist means to deliver the heated slab away from said heaters and towardthe mill, and means actuating said first hoist means to deliver anunheated slab to the empty heater and deposit said slab in said emptyheater.
 7. In a system as set forth in claim 4: said hoist means beingmovable along said line above said heaters; an incoming conveyor at oneend of said line for delivering unheated slabs to a position to bepicked up by said first hoist means; and an outgoing conveyor at theopposite end of said line for receiving heated slabs from said secondhoist means.
 8. In a system as set forth in claim 4: control means forreceiving a demand signal from a mill and for determining the locationof completely heated slabs in said heaters; said control means includingmeans actuating a lift means at a selected heater to raise a heatedslab, means actuating said second hoist means to deliver the heated slabof the selected heater to the outgoing conveyor, and means actuatingsaid first hoist means to pick up an unheated slab from the incomingconveyor and deposit said unheated slab in the empty heater.
 9. In asystem as set forth in claim 5: an incoming conveyor disposed adjacentto the incoming end of said line; an outgoing conveyor disposed adjacentto the outgoing end of said line; said transfer means adapted to pick upa slab at said incoming conveyor and deposit a fully heated slab at saidoutgoing conveyor with each indexing movement.
 10. In a system as setforth in claim 9: said overhead transfer means comprising a plurality ofvertically movable fork means connected together in spaced intervalsequal to the spacing between said heaters and conveyors; means forsimultaneously lowering and raising said fork means; means for movingsaid fork means horizontally along said line; said lift means adapted toproject said slabs above said heaters whereby said fork means can beprojected under slabs at said incoming conveyor and said heaters, saidslabs can be raised and moved to the next heater with one slab beingmoved away from said line toward said outgoing conveyor and a new slabbeing introduced into said line, said slabs can be lowered to the liftmeans of the next adjacent heater and said outgoing conveyor
 11. In asystem as set forth in claim 10: means for aligning each slab with eachheater when said slab is deposited upon said lift means in raisedposition prior to said slab being lowered into the heater.